The present invention relates to an induction-heating cooking device incorporating an inverter for household or business use.
In a conventionally developed induction-heating cooking device, as a structure for indicating a portion of the cooking device which is to be heated by a heating coil, light emitting elements, such as LEDs, are installed in the vicinity of the outer perimeter of the heating coil. The LEDs are lighted according to need, such that the portion to be heated is indicated through an insulating plate having light transmissivity.
A conventional heating cooking device 1000 is described with reference to FIG. 10. The heating cooking device 1000 includes: a heating coil table 101; a heating coil 102 provided on the heating coil table 101; a light-transmissive insulating plate 103 provided above the heating coil 102; and output control means 104 which controls electrical conduction to the heating coil 102. The heating cooking device 1000 further includes display means 106 provided at the outer perimeter of the heating coil 102. The display means 106 includes light emitting elements 105. The light emitting elements 105 indicates the position of the heating coil 102 through the insulating plate. As shown in FIG. 10, a plurality of LEDs, which are provided as the light emitting elements 105, are connected by wirings 1001 so as to form an electric serial circuit. The wirings 1001 are provided along the outer perimeter of the heating coil 102.
Heating cooking devices developed in recent years, which use an inverter and to which the principles of induction heating and dielectric heating are applied, have good heating responsivity and heating controllability. In such a cooking device, a temperature detecting element, a weight sensor, and the like, are provided in the vicinity of a position where a pan or food (load) is to be placed, for detecting the temperature of the pan or food and the weight of the food. Adjustment of the power of heat and adjustment of the cooking time are performed according to the detected temperatures and weight, whereby elaborate cooking can be achieved. Further, although fire is not used, a high thermal efficiency is still obtained, and additionally such a cooking device does not substantially pollute air in a room, but can be used safely and maintained to be clean. Such characteristics have received attention, and the demand for such cooking devices has been sharply increasing.
Furthermore, in such a heating cooking device using an inverter, electrical and thermal stresses imposed on a switching element are reduced, whereby the price of the cooking device is decreased, and the reliability of the cooking device is increased. Especially in a multiple-burner induction-heating cooking device, in order to avoid the generation of interference noise generated between pans placed on adjacent burners, the same, constant operation frequency is used for both these burners, and an inverter which operates based on a system, where a plurality of switching elements in one burner are alternately driven, is used.
Hereinafter, an operation of a heating cooking device is described with reference to the drawings. FIG. 11 is a block diagram showing a structure of a conventional heating cooking device 1100. Parts (a) through (f) of FIG. 12 show waveforms in respective sections of this conventional example. FIG. 13 is a load to heating power characteristic graph.
In FIG. 11, reference numeral 31 denotes a commercial power source, and reference numeral 32 denotes a rectifying circuit. Reference numeral 33 denotes an inverter circuit. The inverter circuit 33 includes first switching means 33a and second switching means 33b, a load coil 33c, and a resonant capacitor 33d. The inverter circuit 33 applies a high frequency current to the load coil 33c so as to inductively heat a load pan 34 which is magnetically coupled to the load coil 33c. A control circuit 35 includes: driving means 36 for driving the first switching means 33a and second switching means 33b; level setting means 37 for outputting a digital signal wherein an input current to the inverter circuit 33 becomes a predetermined value; D/A conversion means 38 for converting an output of the level setting means 37 to an analog value; reference oscillation means 39 for outputting a rectangular wave with a fixed High/Low ratio at a constant frequency; signal conversion means 41 for converting an output of the reference oscillation means 39 to a predetermined triangular wave; driving signal generation means 42 for receiving outputs of the D/A conversion means 38 and the signal conversion means 41 and outputting a signal which allows the driving means 36 to output driving signals to the first switching means 33a and second switching means 33b. Furthermore, in this conventional example, a microcomputer 40 includes the level setting means 37 and the reference oscillation means 39. Reference numeral 43 denotes input current detection means. The input current detection means 43 detects an input current to the inverter circuit 33 and outputs the detected value to the microcomputer 40. The microcomputer 40 changes an output value of the level setting means 37 based on this value, thereby controlling an input current to the inverter circuit 33 so as to be a desired value.
An operation of the above structure is described with reference to parts (a) through (f) of FIG. 12 and FIG. 13. The parts (a) through (f) of FIG. 12 show a timing chart illustrating: an output of the reference oscillation means 39; an output of the D/A conversion means 38; an output of the signal conversion means 41; an output of first comparison means 42a; an output of second comparison means 42b; and outputs of first non-conduction time addition means 42c and second non-conduction time addition means 42d. FIG. 13 shows a relationship between a driving time ratio T31/T32, which represents a ratio between a driving time T31 of the first switching means 33a and a driving time T32 of the second switching means 33b, and an input P to the load pan 34.
An operation of the above structure is described. The inverter circuit 33 converts a direct current, which is obtained by rectifying a current from the commercial power source 31 by the rectifying circuit 32, into a high frequency alternating current. The high frequency current is allowed to flow through a resonant loop formed by the load coil 33c and the resonant capacitor 33d, whereby an eddy current is generated in the load pan 34 which is magnetically coupled to the load coil 33c. Joule heat generated due to the eddy current inductively heats the load pan 34.
The microcomputer 40 outputs to the signal conversion means 41 by the reference oscillation means 39 a rectangular wave with a constant High/Low ratio (xe2x80x9c1xe2x80x9d in this example) at a constant frequency at a constant frequency T0 and having a constant amplitude as shown in part (a) of FIG. 12. The signal conversion means 41 converts this rectangular wave to a triangular wave as shown in part (b) of FIG. 12. On the other hand, the microcomputer 40 increases or decreases a digital value output of the level setting means 37 such that an output of the input current detection means 43 becomes a desired value, whereby an analog output level Vo of the D/A conversion means 38 can be set to any voltage between Vl and Vh as shown in part (b) of FIG. 12.
In this conventional example, a case where the output voltage Vo of the D/A conversion means 38 is Vm shown in part (b) of FIG. 12, at which the driving time ratio T31/T32 is X, is considered. The first comparison means 42a compares the output voltage Vo(=Vm) of the D/A conversion means 38 with an output of the signal conversion means 41. The first comparison means 42a outputs High if the output of the signal conversion means 41 is greater than output voltage Vm of the D/A conversion means 38, and Low if the output of the signal conversion means 41 is smaller than output voltage Vo(=Vm) of the D/A conversion means 38, as shown in part (c) of FIG. 12. On the other hand, the second comparison means 42b compares the output voltage Vo(=Vm) of the D/A conversion means 38 with an output of the signal conversion means 41. The second comparison means 42b outputs Low if the output of the signal conversion means 41 is greater than output voltage Vm of the D/A conversion means 38, and High if the output of the signal conversion means 41 is smaller than output voltage Vo(=Vm) of the D/A conversion means 38, as shown in part (d) of FIG. 12. That is, since the second comparison means 42b produces an output logically inverted with respect to the output of the first comparison means 42a, the output of the second comparison means 42b is Low when the output of the first comparison means 42a is High, and the output of the second comparison means 42b is High when the output of the first comparison means 42a is Low.
The first non-conduction time addition means 42c receives the output of the first comparison means 42a, and produces an output having a rising edge delayed from a rising edge of the output of the first comparison means 42a by a first predetermined period Tda, and a falling edge which is in synchronization with a falling edge of the first comparison means 42a, as shown in part (e) of FIG. 12. On the other hand, the second non-conduction time addition means 42d receives the output of the second comparison means 42b, and produces an output having a rising edge delayed from a rising edge of the output of the second comparison means 42b by a second predetermined period Tdb, and a falling edge which is in synchronization with a falling edge of the second comparison means 42b, as shown in part (f) of FIG. 12. These output signals from the first non-conduction time addition means 42c and the second non-conduction time addition means 42d are output to the driving means 36, whereby the first switching means 33a and the second switching means 33b can be driven alternatively at a constant frequency.
Furthermore, setting of the power of heat supplied to the load pan 34 is performed by appropriately setting the output voltage Vo of the D/A conversion means 38 between Vh and Vl. When the output voltage Vo of the D/A conversion means 38 is equal to Vh, the driving time ratio T31/T32 is smaller than X, and the operation is performed at point A of FIG. 13. When the output voltage Vo of the D/A conversion means 38 is equal to Vm, the driving time ratio T31/T32 is equal to X, and the operation is performed at point B of FIG. 13. When the output voltage Vo of the D/A conversion means 38 is equal to Vl, the driving time ratio T31/T32 is greater than X, and the operation is performed at point C of FIG. 13.
As described above, according to a conventional inverter structure and control method, control of input P to the load pan 34 can be performed with a constant oscillation frequency.
However, the heating cooking device 1000 described above with reference to FIG. 10 has the following problems. In the structure shown in FIG. 10, in the case where an induction-heating operation is performed while indicating a portion to be heated, a magnetic flux generated by the heating coil 102 causes induced electromotive force in the wirings 1001 to the light emitting elements 105. As a result, a variation is caused in the brightness of an LED which is used as the light emitting elements 105, erroneous lighting of the LED used as the light emitting elements 105 is caused, or the light emitting elements 105 are broken due to the induced electromotive force which is greater than the voltage that can be withstood by the light emitting elements 105.
Further, power supply to the display means 106 is achieved through a single power source line (wirings 1001). Thus, in the case where the display means 106 needs to display control information from the output control means 104 while indicating a portion to be heated by the heating coil 102, the output of the display means results in an output from which it is difficult to recognize a portion to be heated by the heating coil 102 due to a variation in the brightness, a variation in a flashing frequency, etc. Furthermore, in the case where some trouble occurs in the power supply from the above power source line, display cannot be performed.
In the conventional heating cooking device 1100 shown in FIG. 11, a variation range of the analog output of the D/A conversion means 38 with respect to one digit of the digital output of the level setting means 37 is decreased, whereby a variation range of the driving time ratio T31/T32 is decreased, and a variation range of the heating power to heat the load pan 34 is decreased. In order to obtain a desirable heating power control range, the digital output of the level setting means 37 is from 4 bits to 8 bits. Since the D/A conversion means 38 has resistances arranged in a ladder pattern, it is necessary to provide a number of resistances which is relative to the output bit number of the level setting means 37. Furthermore, since the signal conversion means 41, which converts an output of the reference oscillation means 39 to a predetermined triangular wave, has a circuit structure where a resistance and a capacitor are combined, the number of components of the circuit is increased, and a variation is caused in each of the inputs to the first comparison means 42a and the second comparison means 42b due to a variation in the constant of a resistance or a capacitor. Thus, a timing of the outputs from the first comparison means 42a and the second comparison means 42b is varied. As a result, a driving timing of the first switching means 33a and the second switching means 33b and the driving time ratio T31/T32 are varied. Consequently, the conventional heating cooking device 1100 has problems, such as a large variation in the heating power to heat the load pan 34, a decrease in the controllability, or the like.
Objectives of the present invention are to solve the above problems, and to provide a highly reliable induction-heating cooking device wherein a variation in the brightness of display means, erroneous lighting of the display means, breakage of a light emitting element, which may be caused due to noise of a magnetic flux for induction heating, are prevented even during a heating operation.
Another objective of the present invention is to provide a highly reliable induction-heating cooking device wherein a portion to be heated by a heating coil can be readily recognized by supplying electric power through a plurality of power source lines according to a content output by the display means, and even when a trouble occurs in one power supply line, the display means can perform display using electric power obtained through another power supply line.
Still another objective of the present invention is to provide an easily-handlable, highly-reliable, and less-expensive induction-heating cooking device wherein the number of electronic components is reduced, and variations in the driving timing of the first switching means 33a and the second switching means 33b and the driving time ratio T31/T32 are suppressed, in order to obtain a desirable heating power to heat a load pan with a high accuracy.
An induction-heating cooking device of the present invention includes: an insulating plate which is partially or entirely light-transmissive, and on which an object to be heated is placed; a heating coil provided under the insulating plate, for heating the object to be heated; display means for indicating a portion to be heated by the heating coil through the insulating plate; and output control means for controlling electrical conduction to the heating coil, wherein the display means includes light emitting means which is provided in the vicinity of a magnetic flux generated by the heating coil, and the light emitting means is laid and connected radially along a radial direction of the heating coil for indicating a portion to be heated by the heating coil. With such a structure, the above objectives can be achieved.
The light emitting means may be connected by a plurality of wiring lines; at least one of the wiring lines may indicate a portion to be heated by the heating coil as an output of the display means; and at least one of the wiring lines may display control information from the output control means.
Another induction-heating cooking device of the present invention includes: an insulating plate which is partially or entirely light-transmissive, and on which an object to be heated is placed; a heating coil provided under the insulating plate, for heating the object to be heated; display means for indicating a portion to be heated by the heating coil through the insulating plate; and output control means for controlling electrical conduction to the heating coil, wherein the display means includes light emitting means, and the light emitting means is laid and connected so as to be powered from a plurality of power supply lines, an output of the display means indicates a portion to be heated by the heating coil, and displays control information from the output control means. With such a structure, the above objectives can be achieved.
At least one of the plurality of power supply lines may be formed by a power supply to which electric power is supplied by a trans-coupling to the heating coil.
Still another induction-heating cooking device of the present invention includes: an inverter circuit having first and second switching means; and a control circuit for controlling the inverter circuit, wherein the control circuit includes driving time ratio setting means, and driving means for driving the plurality of switching means, the driving time ratio setting means includes time ratio output means for outputting a drive timing signal which determines a drive time ratio of the first and second switching means based on an input current to the inverter circuit, and signal distribution means for outputting, based on the drive timing signal, first and second drive signals which are used for driving the first and second switching means, the driving time ratio is represented by a ratio of a first set time period T1, during which the first switching means is driven, and a second set time period T2, during which the second switching means is driven, where a sum T of the first set time period T1 and the second set time period T2 is constant, and the driving means alternately drives the first and second switching means based on the first and second driving signals. With such a structure, the above objectives can be achieved.
The first driving signal may begin after a first latency period elapses since a start timing of the first set time period, and end in synchronization with an end of the first set time period; and the second driving signal may begin after a second latency period elapses since an end timing of the first set time period, and end in synchronization with an end of the second set time period.
The time ratio output means may be formed by a microcomputer which has storage means and which operates based on a program stored in the storage means; and the signal distribution means may be formed by a part including a comparator and a capacitor, which do not operate based on a program.
The inverter circuit may further include: first and second resonant capacitors connected to the first and second switching means; and a load coil connected to the first and second switching means.
An induction-heating cooking device of the present invention includes: an inverter circuit having first and second switching means; and a control circuit for controlling the inverter circuit, wherein the control circuit includes driving time ratio setting means, and driving means for driving the plurality of switching means, the driving time ratio setting means includes first time ratio output means for outputting a first time ratio signal which has a constant period T and a first set time period T21, the first set time period T21 being determined based on an input current to the inverter circuit, and second time ratio output means for outputting a second time ratio signal which has the constant period T and a second set time period T22, and the second time ratio output means starts the second set time period T22 after a second latency period Td22 elapses since an end timing of the first set time period T21, and ends the second set time period T22 at a time which is a first latency period Td21 before a next start timing of the first set time period T21, the second time ratio output means determines the second set time period T22 based on the constant period T, the first latency period Td21, the first set time period T21, and the second latency period Td22, and the driving means alternately drives the first and second switching means based on the first and second time ratio signals. With such a structure, the above objectives can be achieved.
The control circuit may further include zero point detection means for detecting a zero point of a commercial power supply; the driving time ratio setting means may be formed by a microcomputer including storage means and calculation means; and the driving time ratio setting means may set the first set time period T21 and the second set time period T22 at a timing corresponding to an output of the zero point detection means.
The storage means may store the first and second latency periods Td21 and Td22; the control circuit further may include latency time change means; and the microcomputer may change at least one of the first latency period Td21 and the second latency period Td22, which are stored in the storage means, according to an output of the latency time change means.
The control circuit may further include operation setting means for setting an operation state of the control circuit; and the microcomputer may change at least one of the first latency period Td21 or the second latency period Td22, which are stored in the storage means, according to an output of the latency time change means, at at least one of a timing when the operation state of the control circuit is changed by the operation setting means, and a timing when the control circuit begins its operation.
According to one aspect of the present invention, there is provided a highly reliable induction-heating cooking device wherein: a crossing angle of a magnetic flux generated by a heating coil and a wiring to light emitting means is small, whereby induced electromotive force generated in the wiring can be suppressed; and a variation in the brightness of display means, erroneous lighting of the display means, and breakage of an element, can be prevented.
According to another aspect of the present invention, there is provided a highly reliable induction-heating cooking device wherein: noise superposed on a wiring is dispersed by dividing the wiring into multiple wiring lines; even when a trouble occurs in one wiring line, a portion to be heated by a heating coil can be indicated by using another wiring line; the portion to be heated by the heating coil can be indicated while preventing a variation in the brightness of display means, erroneous lighting of the display means, and breakage of an element.
According to still another aspect of the present invention, there is provided a highly reliable induction-heating cooking device wherein: in the case where a large electric power is consumed by an output of the display means, electric power can also be supplied via another power supply line; and even when a trouble occurs in one power supply line, a portion to be heated by the heating coil can be indicated using another power supply line.
According to still another aspect of the present invention, there is provided a highly reliable induction-heating cooking device wherein: large electric power can be supplied to the light emitting means according to an output of the heating coil; and even when a trouble occurs in one power supply line, a portion to be heated by the heating coil can be indicated using another power supply line.
According to still another aspect of the present invention, time ratio output means has a function of outputting a signal where a time ratio can be changed at a constant frequency according to a control signal input to driving time ratio setting means. This function can be achieved by a timer function for counting a first time period which corresponds to an output time ratio, and a timer function for counting a second time period which is determined such that the sum of the first time period and the second time period is constant or which corresponds to a constant period. Thus, a signal where the time ratio can be changed at a constant frequency using a digital calculation device, such as a microcomputer, can be readily output. This output signal is distributed by signal distribution means to a plurality of switching means, so as to alternately drive the plurality of switching means. Thus, high speed processing that is difficult to perform at a program processing speed of a microcomputer, or the like, can be performed: for example, the operation can be kept on standby until an applied voltage, which is applied when the switching means are ON or OFF, reaches a predetermined value. Thus, in the driving time ratio setting means, the range of processing which can be achieved by an integrated circuit, such as a microcomputer, is extended, and a portion formed by other components is minimized, so that the degree of integration is increased. With such an arrangement, the driving time ratio setting means is simplified and the size thereof is decreased. The amount of a high-frequency current flowing through a load coil can be controlled by alternately driving a plurality of switching means.
According to still another aspect of the present invention, time ratio output means outputs a single output signal to a signal distribution means. The time ratio of this output signal is changed simply by inputting information about an input current or an output voltage of an inverter circuit (it is only necessary to substantially change a first set time). Thus, the driving time ratio setting means can be integrally formed by another control circuit block and a digital calculation element, such as a microcomputer or the like. Further, a first latency period and a second standby period can be determined based on a single driving time ratio signal having a constant frequency, and a plurality of switching means can be alternately driven. Thus, the operation is on standby until a resonant voltage or current, which is applied when the switching means are ON or OFF, reaches a value suitable to switching, so that a switching mode is optimized. With such an arrangement, an increase of the loss in the switching means is suppressed, and the operation is prevented from going out of a safety operation range, so as not to break the switching means. Furthermore, a signal distribution section which requires high-speed processing is separated, whereby the size of a circuit structure of the driving time ratio setting means can be decreased.